In convection mode, I assume the microwave uses an electrical resistance heating element.

If so they are both the same 'efficiency' i.e. both use eletric resistance heating which is 100% efficient, i.e. all the energy you put in gets turned to heat. The overall system efficiency will be dependant on the size of the heated space and the heat loss (i.e. insulation and air tightness).

Yes. what exciting Friday nights we have.Both are probably about 2kw. The Fan oven will heat up more quickly and cook slightly faster and at a lower temp. If you look on the cooking instructions on most food wraping it will normally have different cooking temps. and times for conventional and fan ovens.